N-tert-alkylamino pyrrolidinylthiocarbonyl sulfides

ABSTRACT

WHERE R is hydrogen or lower alkyl which is useful for accelerating the vulcanization of diene rubber. A compound of the formula

United States Patent 1 1 [11] 3,875,124

Wilder [451 Apr. 1, 1975 1 1 N-TERT-IALKYLAMINO PYRROLIDINYLT HIOCARBONYL SULFIDES Inventor: Gene R. Wilder, Medina, Ohio Assignee: Monsanta Company, St. Louis, Mo.

Filed: Oct. 27, 1972 Appl. No.: 301,649

Related U.S. Application Data Division of Ser. No. 44658, June 8. 1970, Pat. No. 3,709,905.

U.S. Cl. 260/79.5 B, 260/326.83, 260/784 Int. Cl C08d 9/00, C080 11/40 Field of Search 260/795, 784, 793

References Cited UNITED STATES PATENTS 8/1945 Smith, Jr 260/793 Primary Examiner-Christopher A. Henderson [57] ABSTRACT A compound of the formula R CH2 on S where R is hydrogen or lower alkyl which is useful for accelerating the vulcanization of diene rubber.

1 Claim, No Drawings N-TERT-ALKYLAMINO PYRROLIDINYLTHIOCARBONYL SULFIDES This is a division of application Ser. No. 44,658 filed June 8, 1970, now U.S. Pat. No. 3,709,905.

BACKGROUND OF THE INVENTION The sulfenamides derived from dithiocarbamic acids are known to accelerate the vulcanization of rubber: Cooper U.S. Pat. Nos. 2,333,468 and 2,388,236; Carr and Smith U.S. Pat. No. 2,381,392; and Imperial Chemical Industries Limited British Pat. No. 880,912. Cooper pointed out that cyclopentamethylenethiocarbamyl piperidyl sulfide was an especially potent accelerator. The sulfenamides from eyclotetramethylenediothiocarbamic acids (pyrrolidinylthiocarbonyl sulfides) have not been heretofore described. In general, they lack the requisite stability or shelf life for commercial accelerators, but a stable class of improved accelerating properties has now been discovered.

SUMMARY OF THE INVENTION The new accelerators possess the formula 1 CH CH H N S N tert-alkyl CH CH where tert-alkyl designates tertiary-alkyl of 4 to 8 carbon atoms and R is hydrogen or lower alkyl of 1 to 3 carbon atoms.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The new accelerators may be prepared by oxidative condensation of a salt of the dithiocarbamic acid and tert-alkyl amine. The preparation of tert-butylamino-l pyrrolidinylthiocarbonyl sulfide is exemplary.

The dithiocarbamate is prepared in the customary way by adding 76 grams 1.0 mole) of carbon disulfide to a solution of 71 grams (1.0 mole) of pyrrolidine in 400 ml. of 10 percent aqueous sodium hydroxide. tert- Butyl N-chloroamine is prepared by adding 400 ml. of 18 percent sodium hypochloride to 230 grams of tertbutyl amine at 510C. The solution of the dithiocarbamate prepared as described above is then added over a period of minutes to the tert-butyl N-chloroamine. The temperature is allowed to rise at will and reaches about 3540C., after which stirring of the reaction mixture is continued for about an hour. The resulting precipitate is separated by filtration and the wet filter I cake dissolved in petroleum ether and the water layer and insoluble portion separated. The sulfenamide crystallizes upon cooling the petroleum ether solution and is recovered by filtration. There is obtained 78 grams, m.p. 61-2C. Analysis gives 11.75 percent nitrogen and 28.81 percent, 28.05 percent sulfur compared to 12.8 percent nitrogen and 29.4 percent sulfur calculated for C H N S tert-Butylamino 2,5-dimethyl-1-pyrro1idinylthiocarbonyl sulfide is prepared by condensation of tert-butyl N-chloroamine with the sodium salt of 2,5-dimethylpyrrolindinylcarbodithioic acid. tert-Butyl N- chloroamine is prepared by adding 172 ml. of 16.9 percent sodium hypochlorite to 92 grams of tertbutylamine at 08C. The sodium salt of 2,5- dimethylpyrrolidinylearbodithioic acid is prepared by adding 30.4 grams (0.4 mole) of carbon disulfide to 39.7 grams (0.4 mole) of 2,5-dimethylpyrrolidine in 160 grams of 10 percent sodium hydroxide at room temperature. The sodium salt is then added to the chloroamine dropwise in 12 minutes which causes the temperature to rise to 36C. The reaction mixture is cooled to room temperature with stirring for 2 hours. The liquid product is extracted with ether, washed with water, dried, and recovered by vacuum stripping the solvent. Analysis gives 1 1.06 percent nitrogen and 25.96 percent sulfur compared to 11.37 percent nitrogen and 26.02 percent sulfur calculated for C H- N S An oil-extended styrene-butadiene masterbatch is compounded comprising Parts by Weight SBR 1712* 137.5 Carbon black (ISAF) Zinc oxide 3 Stearic acid 1 Aromatic oil softener 1.5 *Styrene-butadiene copolymer rubber made by cold emulsion polymerization using a fatty acid and rosin soap emulsifier and extended with 37.5 parts by weight of highly aromatic processing oil.

To the masterbatch there is added:

Sulfur 2.2 Accelerator The accelerator is selected from the series where n is 4, 5 or 6.

The stocks are vulcanized in the usual manner by heating in a press at 144C. and the modulus of elasticity evaluated at optimum cure. The stocks are also evaluated in the Monsanto Oscillating Disk Rheometer, a curemeter which provides a complete cure curve. The Rheometer is described by Decker, Wise and Guerry, Rubber World, December 1962, page 68. 1 K RMT, and h -t: are from the Rheometer measurements where 1 is the time in minutes for a rise of two Rheometer units above the minimum reading, 1,, is the time in minutes required to obtain a torque percent of the maximum. The difference, -t is a measure of rate of cure. RMT is the maximum torque and, like the modulus at optimum time of press cure, is a measure of accelerating strength. K is a specific rate constant obtained by assigning zero to the maximum Rheometer reading and increasingly higher numbers to the lower readings. These numbers are plotted on semi-log paper versus time in minutes. On this portion of the cure curve, only one reaction is involved and the cure curve is first order and a straight line is obtained. K is in reciprocal minutes so that larger values mean faster cure. See Coran, Journal of Rubber Chemistry and Technology, p. 689 (1964).

The results are shown in the table below corresponding to the values of 'n in the aforesaid formula:

Modulus of Elasticity Rheometer at 144C. In lbs/in at Designated n Cure Time in Minutes RMT t. t -t- K A similar result is obtained in a silica reinforced natural rubber stock. The sulfur vulcanizable stocks are compounded comprising Parts by Weight Natural rubber smoked sheets 100 Hi-Sil 210* 50 Zinc oxide 5 Stearic acid 3 Sulfur 3 Accelerator 1.5

*Hi-Sil 210 is a precipitated silica sold by PPG Industries.

The stocks are vulcanized in a press at 144C. at optimum cure. The results are shown below:

Modulus of Elasticity Rheometer at 144C.

In lbs/in at Designated n Cure Time in Minutes RM'I' t. t -L;

The tert-butylamino-l-pyrrolidinylthiocarbonyl sulfide vulcanizes rubber and may replace in whole or in part the usual sulfur-vulcanizing agent. For example, to the aforesaid styrene-butadiene masterbatch there is added:

Parts by Weight N- 1 .3-dimethylbutylN -phenyl-p-phenylenediamine 2.0 N-tert-butyl-2-benzothiazole sulfenamide 1.2 tert-hutylamino-l-pyrrolidinylthioearhonyl sulfide 3.0

Styrene-hutadiene rubber EPDM rubber Carbon black (HAF) Zinc oxide Ste-uric acid Aromatic processing oil Sulfur 2.2'-dilhiobis( benzothiazole) 6271 Zine dihutyl dithiophosphate tert-hutylamino-l-pyrrolidinylthiotert-butylamino-Zj-dimethyl-1- Stock A B C Sulfur 2.2 2.2 2.2 N-1.3-dimethylbutyl-N-phenyl-p- 2.0 2.0 2.0 phenylenediamine N-tert-butyl 2-henzothiazolesulfenamide 1.2 tert-hutylamino-1-pyrrolidinylthiocarbonyl 0.5 0.5 sulfide N-(cyelohexylthio)phthalimide The properites of the freshly prepared stock are evaluated by the use of the Monsanto Oscillating Disk Rheometer at 153C. and after storage in an atmosphere of nitrogen for 24 and 48 hours respectively at C.

Rheometer at 153C.

RMT am- 2 2 uuagcd A 58.0 9.4 23.3 .197 B 58.0 7.4 17.3 .299

Aged 24 hours A 55.6 5.9 20.5 .105 B 57.9 5.5 16.1 .248

Aged 48 hours A 54.5 4.5 18.7 .158 B 56.8 4.3 13.8 .268

The properties of the new accelerators in an extended styrene-butadiene copolymer rubber and an EPDM rubber are illustrated in the following stocks:

Stock pyrrolidinylthioearbonyl sulfide Rheomcter at 153C.

RM'l' Rheometer at C.

RMT

The stock is cured in a press at 153C. in 35 minutes giving a modulus at 300 percent elongation of 750 lbslin and a tensile strength at break (750 percent elongation) of 2600 lbs/in? tert-Butylamino-l-pyrrolidinylthioearbonyl sulfide matches the accelerating strength-of the commercial thiazole sulfenamide, N-tert-butyl-Z-benzothiazole sul- Stocks cured with the new accelerators resist aging in oxygen or air, and are much more resistant to post-cure reversion than stocks containing thiazole sulfenamide accelerators.

The sulfcnamides of the invention accelerate the vulcanization of sulfur-vulcanizable diene rubbers, etihen natural or synthetic. These rubbers contain sufficient unsaturation to render them reactive with sulfur. Examples are butyl rubber, cis-4-polybutadiene, ethylenepropylcne terpolymers (EPDM), polyisoprene, butadiene-l ,3 homopolymers, butadiene-l ,3 copolymers with other monomers, for example styrene, acrylonitrile, isobutylene and methylmethacrylate.

Although the invention has been illustrated by typical examples, it is not limited thereto. Changes and modifications of the examples of the invention herein chosen for purposes of disclosure can be made which do not tertiary-butylaminol -pyrrolidinylthiocarbonyl sulfide. l 

1. A PROCESS OF ACCELERATING THE VULCANIZATION OF A SULFURVULCANIZABLE DIENE RUBBER WITH COMPRISES HEATING RUBBER AND SULFUR WITH AN ACCELERATING AMOUNT OF TERTIARY-BUTYLAMINO1-PYRROLIDINYLTHIOCARBONYL SULFIDE. 